Internal combustion engines are generally classified as either constant volume or constant pressure. Otto cycle engines operate by exploding volatile fuel in a constant volume of compressed air while diesel cycle engines burn fuel in a modified cycle, the burning being approximately characterized as constant pressure.
External combustion engines are exemplified by steam engines, steam turbines and gas turbines. It is well known to supply a gas turbine with a gaseous working fluid generated by combusting a fuel with compressed air and to operate various motor devices from energy stored in this high pressure gaseous stream. In these devices, temperature control is usually the result of feeding large quantities of excess compressed air.
It is also known to burn fuel in a chamber and exhaust the combustion products into a working cylinder or chamber, sometimes with the injection of small quantities of water or steam. These may also be classified as external combustion engines.
Some other devices have been proposed in which combustion chambers are cooled by addition of water or steam provided either internally or externally. Still another form of apparatus has been proposed for operation on fuel injected into a combustion cylinder as the temperature falls, having means to terminate fuel injection when the pressure reaches a desired value.
Each of these prior engines has encountered difficulties which limit their general adoption as a power source for the operation of prime movers. Among these difficulties have been the inability of such an engine to meet sudden demand and/or to maintain a constant working temperature or pressure as may be required for efficient operation of such an engine.
Furthermore, control of such engines has been inefficient, and the ability of the gas generator to maintain itself in standby condition has been wholly inadequate. In all practical applied engine configurations the requirement for cooling the confining walls of the work cylinders has resulted in loss of efficiency and a number of other disadvantages previously inherent in internal combustion engines.
The present invention overcomes the limitations of the prior art described above. First, the requirement of large amounts of excess compressed air or external liquid cooling is eliminated by injecting water directly into the combustion chamber to control the temperature of the resulting working fluid. When water is injected it is converted instantaneously into steam in the combustion chamber, and it becomes a component of the working fluid itself, thus increasing the mass and volume of the working fluid without mechanical compression.
In the present invention, independent control of the a) combustion flame temperature b) combustion chamber temperature profile by liquid water injection and c) fuel to air ratio allows the physical properties of the working fluid to be optimized for high efficiency operation. Reducing or eliminating excess air, thus limiting the availability of excess oxygen, and controlling the flame temperature and combustor temperature profile also prevents the formation of NO.sub.x, and favors the complete conversion of burning fuel to CO.sub.2, minimizing CO production.
The present invention also utilizes high pressure ratios as a way of increasing efficiency and horsepower while simultaneously lowering specific fuel consumption ("SFC"). When water is injected and converted into steam in the combustion chamber of the present invention, it acquires the pressure of the combustion chamber. It should be noted that the pressure of the combustion chamber is acquired by the steam irrespective of the pressure ratio of the engine. Thus, a higher pressure ratio can be obtained in the engine without expending additional work for performing compression for new steam or water injection. Because of the injection of massive amounts of water in the present invention, there is no need to compress more air than needed for combustion, this excess air typically used in prior art systems for cooling. The elimination of this requirement results in an enormous energy savings to the system and a significant increase, without additional consumption of fuel, in the available shaft horsepower without increasing turbine speed.
Water injection, as taught in the present invention, provides several advantages over the prior art. First, a minimal amount of additional work is required to pressurize water above the combustion chamber pressure. In steam injection system significant work must be expended to raise the steam to a pressure above that of the combustion chamber. Likewise, excess air requires additional work be expended to raise the feed air to higher pressures to produce additional working fluid mass. Furthermore, when water is injected and converted to steam in the present invention, it acquires the pressure of the combustion chamber without additional work. This steam also has constant entropy and enthalpy.
In the present invention excess (waste) heat from combustion is used to convert injected water to steam, thus increasing the working fluid pressure and mass of the working fluid without mechanical compression of excess air. In contrast, in a typical Brayton Cycle Turbine, 66%-75% of the mechanically compressed air is used to dilute the products of combustion in order to reduce the temperature of the working fluid to the desired Turbine Inlet Temperature ("TIT").
The steam generated by vaporization of the injected water can at least double the mass of the combustion generated working fluid and increase the net horsepower by 15% or more. Therefore, the water can be seen to serve as a fuel in this new thermodynamic system because it supplies pressure, mass, and energy to the system, resulting in an increased efficiency of the present system.
The cycle of the present invention may be open or closed with respect to water. That means that the air and water may be exhausted (open) or recovered and recycled (closed). Desalination or water purification can be a byproduct of electric power generation from a stationary installation or water borne ships, where the cycle is open as to air but closed as to the desalinated water recovery. Marine power plants, industrial applications, drinking water and irrigation water clean up and recovery systems are also viable applications.
The present cycle can also be employed in the closed cycle phase in mobile environments, e.g. autos, trucks, buses, rail locomotives, marine craft, commuter aircraft, general aviation and the like.